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General criteria 
Disinfectants and disinfectant by-products
Extracted from: 
Guidelines for drinking-water quality, 2nd ed. 
Vol. 2 Health criteria and other supporting information, 1996 (pp. 940-949) and Addendum to Vol. 2 . 1998 (pp. 281-283)
Geneva, World Health Organization.

Disinfectants Guideline value (mg/litre) Remarks
monochloramine 3  
di- and trichloramine   NAD
chlorine 5 ATO. For effective disinfection there should be a residual concentration of free chlorine of =0.5 mg/litre after at least 30 minutes contact time at pH <8.0
chlorine dioxide   A guideline value has not been established because of the rapid breakdown of chlorine dioxide and because the chlorite guideline value is adequately protective for potential toxicity from chlorine dioxide
iodine   NAD
Disinfectant by-products Guideline value (µg/litre) Remarks
bromate 25b (P) For 7 × 10-5 excess risk
chlorate   NAD
chlorite 200 (P)  
2-chlorophenol   NAD
2,4-dichlorophenol   NAD
2,4,6-trichlorophenol 200b For excess risk of 10-5, ATO
formaldehyde 900  
trihalomethanes   The sum of the ratio of the concentration of each to its respective guideline value should not exceed 1
bromoform 100  
dibromochloromethane 100  
bromodichloromethane 60b For excess risk of 10-5
chloroform 200  
Chlorinated acetic acids    
monochloroacetic acid   NAD
dichloroacetic acid 50 (P)  
trichloroacetic acid 100 (P)  
chloral hydrate (trichloroacetaldehyde) 10 (P)  
chloroacetone   NAD
Halogenated acetonitriles    
dichloroacetonitrile 90 (P)  
dibromoacetonitrile 100 (P)  
bromochloroacetonitrile   NAD
trichloroacetonitrile 1 (P)  
cyanogen chloride (as CN) 70  
chloropicrin   NAD
a (P) — Provisional guideline value. This term is used for constituents for which there is some evidence of a potential hazard but where the available information on health effects is limited; or where an uncertainty factor greater than 1000 has been used in the derivation of the tolerable daily intake (TDI). Provisional guideline values are also recommended: (1) for substances for which the calculated guideline value would be below the practical quantification level, or below the level that can be achieved through practical treatment methods; or (2) where disinfection is likely to result in the guideline value being exceeded.

b For substances that are considered to be carcinogenic, the guideline value is the concentration in drinking-water associated with an excess lifetime cancer risk of 10-5 (one additional cancer per 100 000 of the population ingesting drinking-water containing the substance at the guideline value for 70 years). Concentrations associated with estimated excess lifetime cancer risks of 10-4 and 10-6 can be calculated by multiplying and dividing, respectively, the guideline value by 10.

In cases in which the concentration associated with an excess lifetime cancer risk of 10-5 is not feasible as a result of inadequate analytical or treatment technology, a provisional guideline value is recommended at a practicable level and the estimated associated excess lifetime cancer risk presented.

It should be emphasized that the guideline values for carcinogenic substances have been computed from hypothetical mathematical models that cannot be verified experimentally and that the values should be interpreted differently from TDI-based values because of the lack of precision of the models. At best, these values must be regarded as rough estimates of cancer risk. However, the models used are conservative and probably err on the side of caution. Moderate short-term exposure to levels exceeding the guideline value for carcinogens does not significantly affect the risk.

c NAD — No adequate data to permit recommendation of a health-based guideline value.

d ATO — Concentrations of the substance at or below the health-based guideline value may affect the appearance, taste, or odour of the water.

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